high-Q Photonic Crystal Nanocavity Research Articles

Electrically controlled on-demand photon transfer between high-Q photonic crystal nanocavities on a silicon chip

Optical buffer memories, which do not rely on an intermediate conversion between optical and electrical signals, can be used to realize optical networks with low latency and low energy consumption. Photonic-crystal nanocavities can confine photons in a very small region for a long time, and thus may be used as core components of such optical buffer memories. However, a scalable method for on-demand photon transfer between nanocavities is required. Here we demonstrate a photonics–electronics integration solution that realizes electrical control of a coupled ultrahigh-quality-factor nanocavity system on a silicon chip. In this system, the photons confined in one of the two storage nanocavities can be transferred to the other storage nanocavity by applying a voltage pulse to the control cavity. A transfer efficiency of 76% and a cavity photon lifetime of 1.3 ns after the transfer are achieved. Researchers demonstrate the transfer of photons from one storage nanocavity into another by applying a voltage pulse. A transfer efficiency of 76% is achieved.

Gas sensing performance of high-Q photonic crystal nanocavities based on a silicon-on-insulator platform

We have proposed and theoretically analyzed the gas sensing performance of the photonic crystal (PhC) nanocavities based on a silicon-on-insulator platform. To assess the gas sensing performance of the proposed PhC nanocavities, the effect of the etch-depth of the circular air holes in the substrate on the quality factor, mode volume, and resonant wavelength have been analyzed. Numerical analysis carried out using the three-dimensional finite-difference time-domain method and filter diagonalization approach shows that the etch-depth significantly perturbs the electric field profile of the original cavity mode. By tuning this parameter, the antinodes of the electric fields are relocated to the air regions of the etch-depth, which leads to an increase in the quality factor and reduction in the mode volume. In this case, the quality factor is found to increase with increasing etch-depth, but still remains as high as 5170 with a small modal volume of $$0.95~(\lambda /n)^{3}$$ . In addition, using the perturbation method, we have demonstrated that the proposed PhC nanocavities possess the capability of detecting the change in the refractive index of the surrounding gas target with a high sensitivity of 322 nm/refractive index unit (RIU) and a detection limit of $$10^{-3}\,RIU$$ . We believe that our proposed PhC nanocavities, which exhibit excellent sensing performances, ultra-small mode volume, and a compact footprint, may offer the potential to develop on-chip sensing devices for applications in gas detection.

Analysis of high-Q photonic crystal L3 nanocavities designed by visualization of the leaky components.

We experimentally study photonic crystal L3 nanocavities whose design Q factors (Qdesign) have been improved with the visualization of leaky components design method. The experimental Q values (Qexp) are monotonically increased from 6,000 to 2,100,000 by iteratively modifying the positions of some of the air holes, as determined by the referred design method. We investigate the Qexp tolerance to imperfections in the fabricated samples, which reveals that the cavities improved by the visualization method tend to lose some tolerance to structural differences between the fabricated samples and the design values.

Nonresonant Excitation Inside an Ultrahigh- <inline-formula> <tex-math notation="LaTeX">$Q$</tex-math></inline-formula> Nanocavity

Achieving on-chip optical wavelength conversion is a long-pursued object with fundamental difficulty in integrated photonics. As a step toward this goal, we theoretically and numerically demonstrate that wavelength conversion can be realized in a high-Q photonic crystal nanocavity, without any phase matching and high power requirement. The wavelength conversion efficiency of nearly 100% is achieved for a broad conversion range, and the mechanism is attributed to the dynamic interaction between the trapped light and an ultrahigh-Q cavity.

CMOS compatible high-Q photonic crystal nanocavity fabricated with photolithography on silicon photonic platform

Progress on the fabrication of ultrahigh-Q photonic-crystal nanocavities (PhC-NCs) has revealed the prospect for new applications including silicon Raman lasers that require a strong confinement of light. Among various PhC-NCs, the highest Q has been recorded with silicon. On the other hand, microcavity is one of the basic building blocks in silicon photonics. However, the fusion between PhC-NCs and silicon photonics has yet to be exploited, since PhC-NCs are usually fabricated with electron-beam lithography and require an air-bridge structure. Here we show that a 2D-PhC-NC fabricated with deep-UV photolithography on a silica-clad silicon-on-insulator (SOI) structure will exhibit a high-Q of 2.2 × 105 with a mode-volume of ~1.7(λ/n)3. This is the highest Q demonstrated with photolithography. We also show that this device exhibits an efficient thermal diffusion and enables high-speed switching. The demonstration of the photolithographic fabrication of high-Q silica-clad PhC-NCs will open possibility for mass-manufacturing and boost the fusion between silicon photonics and CMOS devices.

Raman shift and strain effect in high-Q photonic crystal silicon nanocavity.

We have precisely measured the Raman shift of photonic crystal silicon heterostructure nanocavities for Raman laser applications. We utilized a near-infrared excitation laser of wavelength 1.42 μm in order to avoid local sample heating and exploited two high-Q nanocavity modes to calibrate the Raman frequency. The measured Raman shift was 15.606 THz (520.71 cm(-1)) with a small uncertainty of 1.0 × 10(-3) THz. In addition, we investigated the compressive stress generated in a photonic crystal slab in which a ~5.1 × 10(-3) THz blue shift of the Raman peak and a slight warpage of the slab were observed. We also demonstrated that the stress could be eliminated by using a cantilever structure.

Broad-bandwidth, high-efficiency multiwavelength conversion in a high-Q photonic crystal resonator.

We analytically and numerically demonstrate that multiwavelength conversion can be realized in a high-Q photonic crystal nanocavity. With the help of a dynamic-phase-shift effect induced by bandgap-multireflection, the wavelength conversion efficiency of nearly 100% is achieved for a broad conversion range over several hundreds of nanometers, which is much larger than the reported results obtained by other linear methods (e.g., adiabatic wavelength conversion). This approach may open a way for the study of on-chip ultralow-power optical communications and quantum information processing.

High-Q Photonic Crystal Nanocavities on 300 mm SOI Substrate Fabricated With 193 nm Immersion Lithography

On-chip 1-D photonic crystal nanocavities were designed and fabricated in a 300 mm silicon-on-insulator wafer using a CMOS-compatible process with 193 nm immersion lithography and silicon oxide planarization. High quality factors up to 105 were achieved. By changing geometrical parameters of the cavities, we also demonstrated a wide range of wavelength tunability for the cavity mode, a low insertion loss and excellent agreement with simulation results. These on-chip nanocavities with high quality factors and low modal volume, fabricated through a high-resolution and high-volume CMOS compatible platform open up new opportunities for the photonic integration community.

An on-chip coupled resonator optical waveguide single-photon buffer

Integrated quantum optical circuits are now seen as one of the most promising approaches with which to realize single-photon quantum information processing. Many of the core elements for such circuits have been realized, including sources, gates and detectors. However, a significant missing function necessary for photonic quantum information processing on-chip is a buffer, where single photons are stored for a short period of time to facilitate circuit synchronization. Here we report an on-chip single-photon buffer based on coupled resonator optical waveguides (CROW) consisting of 400 high-Q photonic crystal line-defect nanocavities. By using the CROW, a pulsed single photon is successfully buffered for 150 ps with 50-ps tunability while maintaining its non-classical properties. Furthermore, we show that our buffer preserves entanglement by storing and retrieving one photon from a time-bin entangled state. This is a significant step towards an all-optical integrated quantum information processor.

High-Q photonic crystal slab nanocavity with an asymmetric nanohole in the center for QED

We present a new approach which allows one to insert a silica nanosphere with a single quantum dot into a high Q photonic crystal slab nanocavity with an asymmetric nanohole in the center. The high Q cavity is optimized by adjusting air holes around the L3-type cavity based on three-dimensional finite-difference time-domain simulation. High Q value of 48 700 in this asymmetric cavity is achieved. The performance of the cavity with an assumed silica sphere containing a single quantum dot in the nanohole is also discussed, in which the Q factor can reach 5×104 and modal volume V is 0.048μm3 (∼0.62(λ0/n)3). It is found that the electric field intensity in the nanohole is much stronger than the maximum electric field in the cavity without a nanohole. This makes it possible to locate the precise position of the quantum dot with respect to the cavity mode electric maximum. This system provides a good candidate for realizing a strong interaction between a quantum dot and cavity for the study of cavity quantum electrodynamics.

Electro-optic adiabatic wavelength shifting and Q switching demonstrated using a p-i-n integrated photonic crystal nanocavity

We demonstrate adiabatic wavelength shifting by electro-optic modulation, using a p-i-n integrated high-Q photonic crystal nanocavity. The wavelength of the trapped light is adiabatically shifted by modulating the resonance of the cavity faster than the photon lifetime. The cavity resonance is changed by injecting electrons through a p-i-n junction to reduce the refractive index. In addition, we employ adiabatic wavelength shifting in a demonstration of dynamic Q tuning by electro-optic modulation.

All-silicon sub-Gb/s telecom detector with low dark current and high quantum efficiency on chip

We demonstrate channel selective 0.1-Gb/s photoreceiver operation at telecom wavelength using a silicon high-Q photonic crystal nanocavity with a laterally integrated p-i-n diode. Due to the good crystal property of silicon the measured dark current is only 15 pA. The linear and nonlinear characteristics are investigated in detail, in which we found that the photocurrent is enhanced of more than 105 due to the ultrahigh-Q (Q≃105). With the help of two-photon absorption, which is visible at a surprisingly low input power of 10−8 W, the quantum efficiency of this device reaches ∼10%.

Low power and fast electro-optic silicon modulator with lateral p-i-n embedded photonic crystal nanocavity

We have fabricated high-Q photonic crystal nanocavities with a lateral p-i-n structure to demonstrate low-power and high-speed electro-optic modulation in a silicon chip. GHz operation is demonstrated at a very low (microW level) operating power, which is about 4.6 times lower than that reported for other cavities in silicon. This low-power operation is due to the small size and high-Q of the photonic crystal nanocavity.

Optical Force on Dielectric Nanorods Coupled to a High-Q Photonic Crystal Nanocavity

It is of particular importance to bridge nanophotonics and nanomechanics by utilizing near-field-induced gradient forces to manipulate dielectric objects. On the basis of the finite-difference time-domain method, we theoretically study nanocavity-resonator-induced optical forces on different dielectric nanorods. The optical system consists of a nanorod which is optically coupled to a photonic crystal slab with a predesigned L3 nanocavity that has a resonant mode of high-quality factor Q ≈ 104 and small modal volume 0.1 μm3. Tunable attractive and repulsive (bipolar) optical forces on the nanorod are discovered, which crucially depend on the size of the nanorod and its separation from the slab. The magnitude of the force is revealed to be on the order of 103 pN with source irradiance I = 10 mW/μm2 for a nanorod of size around 200 × 100 × 100 nm3 at a separation d = 100 nm. The results are compared with those by the Rayleigh scattering approximation, which suggests that the optical force is dominated by the gradient force due to the strong local field around the nanocavity. We further demonstrate the optomechanical stability of the system. Such a system provides a promising integrated on-chip platform for all-optical operation of nanomechanical devices.

Light scattering and Fano resonances in high-Q photonic crystal nanocavities

The authors show that light scattering from high-Q planar photonic crystal nanocavities can display Fano-like resonances corresponding to the excitation of localized cavity modes. By changing the scattering conditions, we are able to tune the observed lineshapes from strongly asymmetric and dispersivelike resonances to symmetric Lorentzians. Results are interpreted according to the Fano model of quantum interference between two coupled scattering channels. Combined measurements and line shape analysis on a series of silicon L3 nanocavities as a function of nearby hole displacement demonstrate that Q factors as high as 1.1×105 can be directly measured in these structures. Furthermore, a comparison with theoretically calculated Q factors allows to extract the rms deviation of hole radii due to weak disorder of the photonic lattice.

高Q値フォトニック結晶微小光共振器における光学非線形

高Q値フォトニック結晶微小光共振器における光学非線形

Ultrahigh-Q two-dimensional photonic crystal slab nanocavities in very thin barriers

We demonstrate that width-modulated line-defect nanocavities in photonic crystals with long air slots on either side can maintain an ultrahigh Q even with very thin in-plane photonic crystal (only several rows of air holes). Although it is commonly believed that high-Q photonic crystal nanocavities require relatively thick in-plane barriers, surprisingly these nanocavities fabricated in silicon photonic crystals exhibit an ultrahigh Q (>106) even with very thin barriers. This design may be useful for various nanocavity applications.

Ultra high-Q photonic crystal nanocavity design: The effect of a low-ε slab material

We analyze the influence of the dielectric constant of the slab on the quality factor (Q) in slab photonic crystal cavities with a minimized vertical losses model. The higher value of Q in high-epsilon cavity is attributed to the lower mode frequency. The Q ratio in a high-epsilon (silicon) vs. low-epsilon (diamond) slab is examined as a function of mode volume (V(m)). The mode volume compensation technique is discussed. Finally, diamond cavity design is addressed. The analytical results are compared to 3D FDTD calculations. In a double heterostructure design, a Q approximately 2.6 x 10(5) is obtained. The highest Q approximately 1.3 x 10(6) with V(m)=1.77 x (lambda/n)(3) in a local width modulation design is derived.

Nanocrystals in silicon photonic crystal standing-wave cavities as spin-photon phase gates for quantum information processing

By virtue of a silicon high-Q photonic crystal nanocavity, we propose and examine theoretically interactions between a stationary electron spin qubit of a semiconductor nanocrystal and a flying photon qubit. Firstly, we introduce, derive, and demonstrate the explicit conditions toward realization of a spin-photon phase gate, and propose these interactions as a generalized quantum interface for quantum information processing. Secondly, we examine single-spin-induced reflections as direct evidence of intrinsic bare and dressed modes in our coupled nanocrystal-cavity system.

Coupling quantum dot spins to a photonic crystal nanocavity

We present a method that allows for deterministic coupling of charge-tunable quantum dots to high-Q photonic crystal nanocavity modes. The realization of cavity-mediated coherent coupling of two distant spins is hindered by large fluctuations in quantum dot optical (trion) transition energy and interdot separation. We show that flexible cavity design and gate-voltage-tunable trion transitions in quantum dot molecules can be used to overcome these limitations and to achieve conditional quantum dynamics of two confined spins.